In dogs and rats a dose-dependent decrease in CBF and CMRO2, associated with an increase in CVR has been observed after bolus injection of thiopentone (Michenfelder 1974, Carlsson et al. 1976, Stullken et al. 1977), and phenobarbitone (Nilsson and Siesjö 1975). Through the action of barbiturate on CVR and CBV, ICP will decrease. The suppression of CMRO2 by thiopentone injection reach a plateau of 50% of control, when EEG is isoelectric (Michenfelder 1974, Kassell et al. 1980, Steen et al. 1983). However, in dogs subjected to thiopentone combined with hypothermia to 30 C, CMRO2 decreases to about 70% of control values (Lafferty et al. 1978). At an even higher degree of hypothermia (14–18 C), EEG becomes isoelectric and CMRO2 is reduced to 7–14% of control. Under these circumstances CMRO2 is unaffected by barbiturate (Steen et al. 1983). During continuous thiopentone infusion in dogs and goats, loss of consciousness occurs when CBF and CMRO2 are reduced by 23–30% and emergence from anaesthesia is observed while CMRO2 is still depressed by about 20% (Stullken et al. 1977, Albrecht et al. 1977).
KeywordsNitrous Oxide Severe Head Injury Cerebral Vasodilator Hypnotic Agent Thiopentone Anaesthesia
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